In a subscriber television system, an emergency alert system is used to warn subscribers of severe weather or of national emergencies. Upon receiving an emergency alert message, the subscriber television system must integrate the message into the television signal for delivery and display to the subscribers. Emergency alert systems are well established in analog subscriber television systems. The transition from analog to digital subscriber television systems typically requires the replacement of the supporting auxiliary equipment, such as the emergency alert messaging system. This is because the methods and requirements for inserting an Emergency Alert Message (EAM) into an analog system differ from those for inserting an EAM into a digital system.
A typical method of inserting an emergency alert message in an analog system is illustrated in FIG. 1. Current analog subscriber television systems 101 receive an emergency alert signal at an Emergency Alert System (EAS) receiver 105. An Emergency Alert Controller (EAC) 106, which is interfaced to or contained within the EAS, allows the analog subscriber television system operator to control the display parameters of the emergency alert messages. In the headend 103 of the analog subscriber television system 101, the emergency alert message is overlaid on the desired channel(s) by inputting the message into the modulator 107 (1-n) that processes the desired channel's signal. The signal is then combined in combiner 109 and transmitted over a transmission medium 110 to a subscriber location 120 with the emergency alert message overlaid on the channel.
In a digital subscriber television system, the system usually carries a greater number of channels and each modulator typically processes a multiplexed data stream that includes encoded data for multiple channels. An attempt to make the digital system work like the analog system would have the EAM being input into the QAM modulator, which would then have to overlay the EAM on the desired channels within the multi-channel signal. This would require the modulator to perform the additional tasks of de-multiplexing, decoding, overlaying, re-encoding, and re-multiplexing the digital data stream. The various types of digital subscriber television systems have more efficient methods of transmitting information to the subscriber equipment once the information is input into the digital subscriber television system. An EAM needs to be input into a digital subscriber television system so that the digital subscriber television system can use the method most efficient for that particular type of digital subscriber television system.
The various digital subscriber television systems use a wide variety of different data formats for both text and audio data. Any method, system, or message format for the inputting of emergency alert messages into a digital subscriber television system needs to be able to work with multiple data formats. For example, one system might use a Hyper Text Markup Language (HTML) format for text data and other systems might employ an American Standard Code for Information Interchange (ASCII) format.
Thus, there is a need for an efficient method, system, and message format that will allow the inputting of emergency alert messages into a digital subscriber television system rather than an analog modulator. Such an efficient method, system, and message format should support a wide variety of text and audio formats.